A ram boring device is known from EP-A- 0 361 805 equal to U.S. Pat. No. 4,907,658 as well as from DE-A- 39 00 122 in which the receiving room for the position transmitter is arranged in the region of the tip of the displacement head. This transmitter makes it possible to follow the actual progress of the earth displacement boring since the position as well as the depth of the ram boring device can be ascertained with the help of the position transmitter. Thus earth displacement boring can be carried out under difficult conditions over or under and past crossing conductors without the upper surface of the earth in the vicinity of the crossing conductors having to be dug up.
The arrangement of the position transmitter at the forwardmost part of the displacement head has the advantage that the position of the point of the ram boring apparatus can be ascertained. An essential drawback of this known arrangement, however, lies in that the position transmitter can only be poorly protected against the dynamic impacts of the ram apparatus. Therefore the transmitter has only a very limited service life. It must frequently be replaced already after a few earth borings. Since when a defect of the transmitter occurs it generally appears during an earth boring operation under the load of the impacts of the ram apparatus, the involved earth boring operation frequently cannot reliably be carried through to its end.
A further disadvantage of the known construction resides in that because of the necessary relative small outer diameter of the displacement head in its forward region the strength of the wall surrounding the transmitter is relatively low. Accordingly the longitudinal slots in the chisel nose or point of the displacement head must be relatively Small to assure a sufficient rigidity of the chisel point or of the displacement head. Because of the small slots, however, up to seventy percent (70%) of the transmission output is lost. This limits considerably the depth to which the ram boring device can be reliably placed.
Finally, the construction according to DE-A- 3 900 122, for example, has also the disadvantage that the transmitter is inserted into a bore extending inwardly from the front of the chisel point. The closure element closing this bore is in direct contact with the earth and is exposed to stones and similar impediments. Above all, in the destruction of impediments the closure element is extraordinarily strained and can easily be damaged.